The Turndown of the Baryonic Tully–Fisher Relation and Changing Baryon Fraction at Low Galaxy Masses
The Turndown of the Baryonic Tully–Fisher Relation and Changing Baryon Fraction at Low Galaxy Masses
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DOI：
10.3847/1538-4357/ac9285
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发表时间：
2022-03
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影响因子：
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通讯作者：
K. McQuinn;E. Adams;J. Cannon;John H. Fuson;E. Skillman;A. Brooks;K. Rhode;M. Haynes;J. Inoue-J.-I
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作者：
K. McQuinn;E. Adams;J. Cannon;John H. Fuson;E. Skillman;A. Brooks;K. Rhode;M. Haynes;J. Inoue-J.-I
现代星系中重子物质与暗物质的比例限制了星系形成理论，并可以通过重子塔利-费舍尔关系（BTFR）经验地确定，该关系将星系的重子质量（M bary）与其最大旋转速度（V max）进行比较。BTFR在M bary > 108 M bary时得到了很好的确定，但由于样本量小以及在该状态下测量旋转速度的挑战，在较低质量下的限制很差。对于25个具有高质量观测数据的星系，M bary = 108 M bary，我们用红外和H i观测估算了M bary，用H i气体自转估算了Vmax.许多Vmax值是下限，因为在检测到的H i盘（R max）的边缘处速度仍在上升;因此，我们的大多数样品的速度低于在更高质量下从BTFR外推的预期速度。为了估计V最大值，我们将每个星系映射到暗物质晕，假设有和没有核心的密度分布。与未取芯剖面相比，我们发现取芯剖面旋转曲线在R max值处仍在上升，与数据相似。当我们将从核心密度分布得到的Vmax值与我们的M bary测量值进行比较时，我们发现在低质量下BTFR的下降与Λ冷暗物质的预测一致，并且意味着重子分数为宇宙值的1%-10%。虽然我们受到样本大小和将测量的旋转速度映射到理论旋转曲线的假设的限制，但我们的结果表明，星系形成效率在质量低于M bary <$108 M <$，对应于M 200 <$1010 M <$时下降。
The ratio of baryonic-to-dark matter in present-day galaxies constrains galaxy formation theories and can be determined empirically via the baryonic Tully–Fisher relation (BTFR), which compares a galaxy’s baryonic mass (M bary) to its maximum rotation velocity (V max). The BTFR is well determined at M bary > 108 M ⊙, but poorly constrained at lower masses due to small samples and the challenges of measuring rotation velocities in this regime. For 25 galaxies with high-quality data and M bary ≲ 108 M ⊙, we estimate M bary from infrared and H i observations and V max from the H i gas rotation. Many of the V max values are lower limits because the velocities are still rising at the edge of the detected H i disks (R max); consequently, most of our sample has lower velocities than expected from extrapolations of the BTFR at higher masses. To estimate V max, we map each galaxy to a dark matter halo assuming density profiles with and without cores. In contrast to noncored profiles, we find the cored profile rotation curves are still rising at R max values, similar to the data. When we compare the V max values derived from the cored density profiles to our M bary measurements, we find a turndown of the BTFR at low masses that is consistent with Λ cold dark matter predictions and implies baryon fractions of 1%–10% of the cosmic value. Although we are limited by the sample size and assumptions inherent in mapping measured rotational velocities to theoretical rotation curves, our results suggest that galaxy formation efficiency drops at masses below M bary ∼ 108 M ⊙, corresponding to M 200 ∼ 1010 M ⊙.